There currently exist a large variety of fittings for use in fluid systems such as hydraulic systems or the like. Many are so-called compression fittings and typically employ a ferrule, which, together with a nut, are disposed on a tube or conduit near an end thereof. An externally threaded sleeve is engaged with the nut, and as the latter is tightened, the ferrule is compressed and slightly deformed into sealing engagement with the tube as well as a surface within the sleeve. There are, of course, a great variety of compression fittings operating on this basic theme, and in general, they work very well for their intended purpose. However, in high pressure applications, difficulty in their use is observed. Similarly, when used in applications requiring occasional or frequent disassembly, they may result in leaky joints.
In particular, if the tube on which the ferrule is receives is too rigid, some difficulty may be be experience in sealing the interface between the tube and the ferrule.
Furthermore, the same can be over or under tightened, depending upon the assembler. In the case of the former, upon disassembly of the joint and reassembly thereof, a difficulty may be experienced in resealing the joint. In the case of the latter, an initial seal may not be obtained.
Frequently, joints of this sort, or joints employing packing may be utilized to seal the interface of a tube of relatively small diameter placed nominally concentrically within a tube of larger diameter. For example, a small diameter tube maybe a so-called "thimble" which receives a sensor which is to be disposed within the larger tube to sense, for example, temperature differences in a fluid in fluid communication with the interior of the larger tube. In some instances, the smaller tube may be part of an electrical heating element or the like. In these instances, the periodic disassembly or maintenance or the like is required, it is highly desirable to provide a reusable fitting having excellent sealing characteristics so as to avoid the difficulties that may occur in the reuse of so-called compression fittings. To avoid the difficulties associated with such fittings, the use of seal rings and flanged couplings have been proposed as well as other forms of packing, including O-rings. However, flanged couplings are difficult to disassemble and reassemble, particularly when one coupling element mounts a thimble. Conventional O-ring configurations are not known to be adapted for concentric tube assemblies in such a fashion that the components may be readily serviced and reused.
Thus, there is a real need for a new and improved fitting that avoids the difficulties encountered with the use of compression fittings, is capable of use in high pressure systems without leakage, and which is easily installed and subsequently serviced.